A Phase-Locked Loop and a Phase-Locking Method

Abstract

The present application discloses a phase-locked loop and a phase-locked method, which includes: a sampling module for acquiring a grid voltage; a first transformation module for converting the grid voltage from a three-phase stationary coordinate system to a two-phase stationary coordinate system through Clarke transformation; a second transformation module for transforming the grid voltage of the two-phase stationary coordinate system to obtain an intermediate rotating variable; an attenuator for processing the intermediate rotating variable through a frequency domain filtering algorithm to attenuate the non-fundamental content to obtain a filtered variable; a first angle module for determining the angle to be adjusted based on the filtered variable; and a second angle module for performing PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle. The present application utilizes an attenuator to attenuate the non-fundamental content of the intermediate rotating variable, and then performs phase-locked calculation using a stable and reliable filtered variable. The calculation is fast, the results are stable and reliable, and fast and accurate phase-locked calculation can be achieved under various conditions where the grid voltage quality is unqualified.

Description

Technical Field

[0001] The present invention relates to the field of power control, and in particular to a phase-locked loop and a phase-locked method. Background Art

[0002] Phase-locked loops (PLLs) are a crucial component of DC transmission systems. Traditional PLLs exhibit certain errors and slow dynamic response when grid voltage quality is substandard. To address this issue, in 2019, Professor Vassilios G. Agelidis and his colleagues proposed an adaptive coupled-delay signal cancellation strategy. This strategy generates amplitude-balanced three-phase voltages and eliminates grid voltage phase deviations, enabling precise phase locking under unbalanced grid voltages and improving system reliability. However, this strategy requires a large number of sensors, limiting its application.

[0003] To address this issue, in 2020, Professor Yongchang Zhang and others proposed a novel model predictive control scheme without grid voltage sensors. This scheme estimates the grid voltage by calculating the grid virtual magnetic flux, and then performs phase-locked calculations on the grid voltage. This scheme reduces the number of sensors and achieves precise phase-locking under unbalanced grid voltages. However, its application scenarios are relatively limited, and it can only be applied to conditions with distorted and unbalanced grid voltages. It will fail when the grid experiences frequency fluctuations and DC bias.

[0004] Therefore, how to provide a solution to the above technical problems is a problem that those skilled in the art need to solve. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a phase-locked loop and phase-locked method to achieve fast and accurate phase locking in various situations. The specific scheme is as follows:

[0006] A phase-locked loop, comprising:

[0007] Sampling module, used to obtain grid voltage;

[0008] A first conversion module, configured to convert the grid voltage from a three-phase stationary coordinate system to a two-phase stationary coordinate system through Clarke transformation;

[0009] a second transformation module, configured to transform the grid voltage of the two-phase stationary coordinate system using the phase-locked angle of the previous cycle to obtain an intermediate rotation variable;

[0010] an attenuator for processing the intermediate rotation variable through a frequency domain filtering algorithm to attenuate non-fundamental wave content to obtain a filtered variable;

[0011] A first angle module, configured to determine an angle to be adjusted according to the filtered variable;

[0012] The second angle module is used to perform PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle.

[0013] Preferably, the second transformation module is specifically used to:

[0014] Calculate according to the intermediate transformation formula to obtain the intermediate rotation variable; the intermediate transformation formula is specifically:

[0015]

[0016] Among them, u α and u β is the grid voltage of the two-phase stationary coordinate system, u1 and u2 are the intermediate rotating variables, is the phase-locked angle of the previous cycle.

[0017] Preferably, the attenuator is specifically used for:

[0018] Calculate according to the attenuation formula to obtain the filtered variable; the attenuation formula is specifically:

[0019]

[0020] Where z is a discrete domain operator, N is a preset constant, and u3 and u4 are filtered variables.

[0021] Preferably, the first angle module is specifically used for:

[0022] Calculate according to the angle formula to obtain the angle to be adjusted; the angle formula is specifically:

[0023]

[0024] in, is the angle to be adjusted.

[0025] Preferably, the second angle module is specifically used for:

[0026] The phase-locked angle of the current cycle is calculated according to the PID formula; the PID formula is specifically:

[0027]

[0028] Where K is the control coefficient, is the phase-locked angle of the current cycle.

[0029] Accordingly, the present application also discloses a phase locking method, comprising:

[0030] Get the grid voltage;

[0031] Converting the grid voltage from a three-phase stationary coordinate system to a two-phase stationary coordinate system through Clarke transformation;

[0032] transforming the grid voltage of the two-phase stationary coordinate system using the phase-locked angle of the previous cycle to obtain an intermediate rotation variable;

[0033] Processing the intermediate rotation variable by a frequency domain filtering algorithm to attenuate non-fundamental wave content to obtain a filtered variable;

[0034] Determining the angle to be adjusted according to the filtered variable;

[0035] Perform PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle.

[0036] Preferably, the process of transforming the grid voltage of the two-phase stationary coordinate system using the phase-locked angle of the previous cycle to obtain an intermediate rotation variable includes:

[0037] Calculate according to the intermediate transformation formula to obtain the intermediate rotation variable; the intermediate transformation formula is specifically:

[0038]

[0039] Among them, u α and u β is the grid voltage of the two-phase stationary coordinate system, u1 and u2 are the intermediate rotating variables, is the phase-locked angle of the previous cycle.

[0040] Preferably, the process of processing the intermediate rotation variable by a frequency domain filtering algorithm to attenuate non-fundamental wave content to obtain a filtered variable includes:

[0041] Calculate according to the attenuation formula to obtain the filtered variable; the attenuation formula is specifically:

[0042]

[0043] Where z is a discrete domain operator, N is a preset constant, and u3 and u4 are filtered variables.

[0044] Preferably, the process of determining the angle to be adjusted according to the filtered variable includes:

[0045] Calculate according to the angle formula to obtain the angle to be adjusted; the angle formula is specifically:

[0046]

[0047] in, is the angle to be adjusted.

[0048] Preferably, the process of performing PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle includes:

[0049] The phase-locked angle of the current cycle is calculated according to the PID formula; the PID formula is specifically:

[0050]

[0051] Where K is the control coefficient, is the phase-locked angle of the current cycle.

[0052] The present application discloses a phase-locked loop (PLL), comprising: a sampling module for acquiring a grid voltage; a first transformation module for converting the grid voltage from a three-phase stationary coordinate system to a two-phase stationary coordinate system through Clarke transformation; a second transformation module for transforming the grid voltage in the two-phase stationary coordinate system using the phase-locked angle of the previous cycle to obtain an intermediate rotating variable; an attenuator for processing the intermediate rotating variable through a frequency domain filtering algorithm to attenuate non-fundamental content to obtain a filtered variable; a first angle module for determining an angle to be adjusted based on the filtered variable; and a second angle module for performing PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle. The present application utilizes an attenuator to attenuate the non-fundamental content of the intermediate rotating variable, so that when the grid voltage has voltage distortion, imbalance, frequency fluctuation, or DC bias, a stable and reliable filtered variable can still be used for phase-locked calculation. The calculation is fast, the results are stable and reliable, and fast and accurate phase-locked calculation can be achieved under various grid voltage quality conditions. The method is simple to implement and has high engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0054] Figure 1 This is a structural distribution diagram of a phase-locked loop in an embodiment of the present invention;

[0055] Figure 2 This is a system flow chart of a phase-locked loop according to an embodiment of the present invention;

[0056] Figure 3 4 is a flow chart of the steps of a phase locking method in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0058] In the existing technology, the adaptive linked delayed signal cancellation strategy requires more sensors and has a limited application range; the method of estimating the grid voltage by calculating the virtual magnetic flux of the grid and then performing phase-locked calculation of the grid voltage requires fewer sensors, but the application scenarios are relatively single and cannot solve situations such as frequency fluctuations or DC bias in the grid.

[0059] This application utilizes an attenuator to attenuate the non-fundamental content of the intermediate rotating variable, so that when the grid voltage has voltage distortion, imbalance, frequency fluctuation or DC bias, phase-locked calculation can still be performed with stable and reliable filtered variables. The calculation is fast and the results are stable and reliable. It can achieve fast and accurate phase-locked calculation under various conditions where the grid voltage quality is unqualified. The method is simple to implement and has high engineering application value.

[0060] The embodiment of the present invention discloses a phase-locked loop, which can be applied to various conventional application scenarios of phase-locked loops, such as flexible direct current transmission systems, see Figure 1 As shown, the phase-locked loop in this embodiment includes:

[0061] Sampling module 1, used to obtain grid voltage;

[0062] A first transformation module 2 is configured to transform the grid voltage from a three-phase stationary coordinate system to a two-phase stationary coordinate system through Clarke transformation;

[0063] The second transformation module 3 is used to transform the grid voltage of the two-phase stationary coordinate system using the phase-locked angle of the previous cycle to obtain an intermediate rotation variable;

[0064] Attenuator 4, used for processing the intermediate rotation variable through a frequency domain filtering algorithm to attenuate the non-fundamental content to obtain a filtered variable;

[0065] A first angle module 5, configured to determine the angle to be adjusted based on the filtered variables;

[0066] The second angle module 6 is used to perform PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle.

[0067] Specifically, the sampling module 1 generally includes a voltage sensor to obtain the grid voltage. The voltage sensor may be a Hall element. The current grid voltage obtained is u in the three-phase stationary coordinate system. a 、u b、u c In the first transformation module 2, Clark transform is used to transform u into a two-phase stationary coordinate system. α 、u β , the specific transformation process is as follows:

[0068]

[0069] Furthermore, the second transformation module 3 is specifically configured to:

[0070] Calculate according to the intermediate transformation formula to obtain the intermediate rotation variable; the intermediate transformation formula is specifically:

[0071]

[0072] Among them, u α and u β is the grid voltage of the two-phase stationary coordinate system, u1 and u2 are intermediate rotating variables, is the phase-locked angle of the previous cycle. It can be understood that the intermediate transformation is similar to the Park transformation Park but there are differences. The intermediate transformation of this embodiment provides feasibility for accurate and rapid component attenuation in the subsequent attenuator 4.

[0073] It is understandable that the attenuation formula is the core processing method of the frequency domain filtering algorithm. Therefore, the attenuator 4 is specifically used to:

[0074] Calculate according to the attenuation formula to obtain the filtered variable; the attenuation formula is as follows:

[0075]

[0076] Where z is a discrete domain operator, N is a preset constant, and u3 and u4 are filtered variables.

[0077] Furthermore, the first angle module 5 is specifically used for:

[0078] Calculate according to the angle formula to obtain the angle to be adjusted; the angle formula is specifically:

[0079]

[0080] in, The angle to be adjusted.

[0081] Furthermore, the second angle module 6 is specifically used for:

[0082] Calculate according to the PID formula to obtain the phase-locked angle of the current cycle; the PID formula is as follows:

[0083]

[0084] Where K is the control coefficient, is the phase-locked angle of the current cycle.

[0085] It can be understood that the PID formula is a traditional phase-locked loop operation formula, but the input in the traditional operation is the phase angle of the real-time grid voltage, while in this embodiment, the input is the angle to be adjusted obtained after processing by the early attenuator 4 and the first angle module 5, which eliminates the negative effects of three-phase imbalance, harmonic interference, frequency fluctuation, DC bias, etc. in the grid voltage, and is more in line with the fundamental characteristics of the current grid voltage. Using the angle to be adjusted to calculate the PID formula can obtain a more accurate phase-locked effect.

[0086] It is understandable that in the control of the next cycle of the phase-locked loop, the phase-locked angle of the current cycle The value of Participate in the calculation of the intermediate transformation formula. For details, see Figure 2 As shown in the system flow chart, the working process of the phase-locked loop is implemented in a closed-loop manner.

[0087] This application utilizes an attenuator to attenuate the non-fundamental content of the intermediate rotating variable, so that when the grid voltage has voltage distortion, imbalance, frequency fluctuation or DC bias, phase-locked calculation can still be performed with stable and reliable filtered variables. The calculation is fast and the results are stable and reliable. It can achieve fast and accurate phase-locked calculation under various conditions where the grid voltage quality is unqualified. The method is simple to implement and has high engineering application value.

[0088] Correspondingly, the embodiment of the present application also discloses a phase locking method, see Figure 3 As shown, including:

[0089] S1: Get the grid voltage;

[0090] S2: Convert the grid voltage from the three-phase stationary coordinate system to the two-phase stationary coordinate system through Clarke transformation;

[0091] S3: Using the phase-locked angle of the previous cycle to transform the grid voltage of the two-phase stationary coordinate system to obtain an intermediate rotating variable;

[0092] S4: Process the intermediate rotation variable through a frequency domain filtering algorithm to attenuate the non-fundamental content and obtain the filtered variable;

[0093] S5: Determine the angle to be adjusted according to the filtered variable;

[0094] S6: Perform PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle.

[0095] The phase-locked method of the present application attenuates the non-fundamental content of the intermediate rotating variable, so that when the grid voltage has voltage distortion, imbalance, frequency fluctuation or DC bias, it can still perform phase-locked calculation with stable and reliable filtered variables. The calculation is fast and the results are stable and reliable. It can achieve fast and accurate phase-locked calculation under various conditions where the grid voltage quality is unqualified. The method is simple to implement and has high engineering application value.

[0096] In some specific embodiments, the process of transforming the grid voltage of the two-phase stationary coordinate system using the phase-locked angle of the previous cycle to obtain the intermediate rotating variable includes:

[0097] Calculate according to the intermediate transformation formula to obtain the intermediate rotation variable; the intermediate transformation formula is specifically:

[0098]

[0099] Among them, u α and u β is the grid voltage of the two-phase stationary coordinate system, u1 and u2 are intermediate rotating variables, is the phase-locked angle of the previous cycle.

[0100] In some specific embodiments, the process of processing the intermediate rotation variable by a frequency domain filtering algorithm to attenuate non-fundamental wave content to obtain a filtered variable includes:

[0101] Calculate according to the attenuation formula to obtain the filtered variable; the attenuation formula is as follows:

[0102]

[0103] Where z is a discrete domain operator, N is a preset constant, and u3 and u4 are filtered variables.

[0104] In some specific embodiments, the process of determining the angle to be adjusted according to the filtered variable includes:

[0105] Calculate according to the angle formula to obtain the angle to be adjusted; the angle formula is specifically:

[0106]

[0107] in, The angle to be adjusted.

[0108] In some specific embodiments, the process of performing PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle includes:

[0109] Calculate according to the PID formula to obtain the phase-locked angle of the current cycle; the PID formula is as follows:

[0110]

[0111] Where K is the control coefficient, is the phase-locked angle of the current cycle.

[0112] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0113] The above is a detailed introduction to a phase-locked loop and a phase-locked method provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A phase-locked loop, characterized in that: include: Sampling module, used to obtain grid voltage; A first conversion module, configured to convert the grid voltage from a three-phase stationary coordinate system to a two-phase stationary coordinate system through Clarke transformation; a second transformation module, configured to transform the grid voltage of the two-phase stationary coordinate system using the phase-locked angle of the previous cycle to obtain an intermediate rotation variable; The second transformation module is specifically configured to: Calculate according to the intermediate transformation formula to obtain the intermediate rotation variable; the intermediate transformation formula is specifically: Among them, u α and u β is the grid voltage of the two-phase stationary coordinate system, u1 and u2 are the intermediate rotating variables, is the phase-locked angle of the previous cycle; an attenuator for processing the intermediate rotation variable through a frequency domain filtering algorithm to attenuate non-fundamental wave content to obtain a filtered variable; Wherein, the attenuator is specifically used for: Calculate according to the attenuation formula to obtain the filtered variable; the attenuation formula is specifically: Where z is the discrete domain operator, N is a preset constant, and u3 and u4 are filtered variables; A first angle module, configured to determine an angle to be adjusted according to the filtered variable; Wherein, the first angle module is specifically used for: Calculate according to the angle formula to obtain the angle to be adjusted; the angle formula is specifically: in, is the angle to be adjusted; The second angle module is used to perform PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle.

2. The phase-locked loop according to claim 1, wherein: The second angle module is specifically used for: The phase-locked angle of the current cycle is calculated according to the PID formula; the PID formula is specifically: Where K is the control coefficient, is the phase-locked angle of the current cycle.

3. A phase-locking method, characterized in that: include: Get the grid voltage; Converting the grid voltage from a three-phase stationary coordinate system to a two-phase stationary coordinate system through Clarke transformation; transforming the grid voltage of the two-phase stationary coordinate system using the phase-locked angle of the previous cycle to obtain an intermediate rotation variable; Wherein, the grid voltage of the two-phase stationary coordinate system is transformed by using the phase-locked angle of the previous cycle to obtain an intermediate rotation variable, including: Calculate according to the intermediate transformation formula to obtain the intermediate rotation variable; the intermediate transformation formula is specifically: Among them, u α and u β is the grid voltage of the two-phase stationary coordinate system, u1 and u2 are the intermediate rotating variables, is the phase-locked angle of the previous cycle; Processing the intermediate rotation variable by a frequency domain filtering algorithm to attenuate non-fundamental wave content to obtain a filtered variable; The step of processing the intermediate rotation variable by a frequency domain filtering algorithm to attenuate non-fundamental content and obtain a filtered variable comprises: the step of processing the intermediate rotation variable by a frequency domain filtering algorithm to attenuate non-fundamental content and obtain a filtered variable comprises: Calculate according to the attenuation formula to obtain the filtered variable; the attenuation formula is specifically: Where z is the discrete domain operator, N is a preset constant, and u3 and u4 are filtered variables; Determining the angle to be adjusted according to the filtered variable; The determining of the angle to be adjusted according to the filtered variable includes: performing calculation according to an angle formula to obtain the angle to be adjusted; the angle formula is specifically: in, is the angle to be adjusted; Perform PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle.

4. The phase-locking method according to claim 3, characterized in that: The process of performing PID adjustment on the angle to be adjusted to obtain the phase-locked angle of the current cycle includes: The phase-locked angle of the current cycle is calculated according to the PID formula; the PID formula is specifically: Where K is the control coefficient, is the phase-locked angle of the current cycle.

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